Clinicopathologic subtype of Alzheimer's disease presenting as corticobasal syndrome

Comparing classic-onset corticobasal syndrome to speech/language-onset corticobasal syndrome

INTRODUCTION

Patients with classic-onset corticobasal syndrome (CBS) present with asymmetric limb apraxia and parkinsonism. We have, however, observed patients who initially present with speech and/or language (SL) problems and several years later develop CBS (i.e., SL-onset CBS). We aimed to compare clinical, neuroimaging and pathological characteristics of classic-onset CBS with SL-onset CBS.

METHODS

We conducted a retrospective cohort study of 62 patients who met criteria for CBS (17 presented with classic-onset CBS and 45 had SL-onset CBS). We compared demographics, clinical characteristics, and grey and white matter volume loss with SPM12 between groups and assessed pathology and corticobasal degeneration (CBD) pathological lesion counts in patients who had died and undergone autopsy.

RESULTS

Median age at CBS diagnosis was 66.4 years in classic-onset CBS and 73.6 years in SL-onset CBS. Classic-onset CBS had higher frequencies of dystonia, myoclonus, and alien limb phenomenon, while SL-onset CBS had a higher frequency of vertical supranuclear gaze palsy. Both groups showed smaller frontoparietal volumes than controls, with SL-onset CBS having greater volume loss in the left supplementary motor area than classic-onset CBS. All three classic-onset CBS cases with autopsy (100 %) had CBD pathology while 8/21 of SL-onset CBS cases (38 %) had CBD. Pathological lesion burden (including astrocytic plaques) did not differ between classic-onset and SL-onset CBS.

CONCLUSION

Classic-onset and SL-onset CBS appear to be different syndromes, with the former being a more profuse motor syndrome. The more widespread volume loss in SL-onset CBS likely reflects longer disease course.

European intersocietal recommendations for the biomarker-based diagnosis of neurocognitive disorders

The recent commercialisation of the first disease-modifying drugs for Alzheimer's disease emphasises the need for consensus recommendations on the rational use of biomarkers to diagnose people with suspected neurocognitive disorders in memory clinics. Most available recommendations and guidelines are either disease-centred or biomarker-centred. A European multidisciplinary taskforce consisting of 22 experts from 11 European scientific societies set out to define the first patient-centred diagnostic workflow that aims to prioritise testing for available biomarkers in individuals attending memory clinics. After an extensive literature review, we used a Delphi consensus procedure to identify 11 clinical syndromes, based on clinical history and examination, neuropsychology, blood tests, structural imaging, and, in some cases, EEG. We recommend first-line and, if needed, second-line testing for biomarkers according to the patient's clinical profile and the results of previous biomarker findings. This diagnostic workflow will promote consistency in the diagnosis of neurocognitive disorders across European countries.

Connectome-based modelling of neurodegenerative diseases: towards precision medicine and mechanistic insight

Neurodegenerative diseases are the most common cause of dementia. Although their underlying molecular pathologies have been identified, there is substantial heterogeneity in the patterns of progressive brain alterations across and within these diseases. Recent advances in neuroimaging methods have revealed that pathological proteins accumulate along specific macroscale brain networks, implicating the network architecture of the brain in the system-level pathophysiology of neurodegenerative diseases. However, the extent to which 'network-based neurodegeneration' applies across the wide range of neurodegenerative disorders remains unclear. Here, we discuss the state-of-the-art of neuroimaging-based connectomics for the mapping and prediction of neurodegenerative processes. We review findings supporting brain networks as passive conduits through which pathological proteins spread. As an alternative view, we also discuss complementary work suggesting that network alterations actively modulate the spreading of pathological proteins between connected brain regions. We conclude this Perspective by proposing an integrative framework in which connectome-based models can be advanced along three dimensions of innovation: incorporating parameters that modulate propagation behaviour on the basis of measurable biological features; building patient-tailored models that use individual-level information and allowing model parameters to interact dynamically over time. We discuss promises and pitfalls of these strategies for improving disease insights and moving towards precision medicine.

How Many Alzheimer-Perusini's Atypical Forms Do We Still Have to Discover?

Alzheimer-Perusini's (AD) disease represents the most spread dementia around the world and constitutes a serious problem for public health. It was first described by the two physicians from whom it took its name. Nowadays, we have extensively expanded our knowledge about this disease. Starting from a merely clinical and histopathologic description, we have now reached better molecular comprehension. For instance, we passed from an old conceptualization of the disease based on plaques and tangles to a more modern vision of mixed proteinopathy in a one-to-one relationship with an alteration of specific glial and neuronal phenotypes. However, no disease-modifying therapies are yet available. It is likely that the only way to find a few "magic bullets" is to deepen this aspect more and more until we are able to draw up specific molecular profiles for single AD cases. This review reports the most recent classifications of AD atypical variants in order to summarize all the clinical evidence using several discrimina (for example, post mortem neurofibrillary tangle density, cerebral atrophy, or FDG-PET studies). The better defined four atypical forms are posterior cortical atrophy (PCA), logopenic variant of primary progressive aphasia (LvPPA), behavioral/dysexecutive variant and AD with corticobasal degeneration (CBS). Moreover, we discuss the usefulness of such classifications before outlining the molecular-genetic aspects focusing on microglial activity or, more generally, immune system control of neuroinflammation and neurodegeneration.

Hippocampal subfield volumetry in corticobasal syndrome of diverse underlying pathologies

INTRODUCTION

Multiple pathologies may underlie corticobasal syndrome (CBS), including Alzheimer's disease (AD). Typical amnestic AD is characterized by early selective hippocampal atrophy. The profile of hippocampal atrophy in AD patients presenting as CBS (CBS-AD), compared to CBS patients of non-AD pathologies (CBS-nAD) and amnestic AD patients, has not been studied.

OBJECTIVES

To compare hippocampal subfield atrophy patterns between CBS-AD, CBS-nAD, typical amnestic AD patients, and control subjects.

METHODS

Automated hippocampal subfield volumetry was performed via the hippocampal subfield segmentation pipeline of Freesurfer 6.0 on 3D T1-weighted images. CBS patients were classified as CBS-AD or CBS-nAD based on CSF AD biomarkers by applying the AT(N) classification system. Mean volumes of nine hippocampal subfields, head-body-tail segments, total hippocampus, and entorhinal and parahippocampal gyrus cortical thickness were measured.

RESULTS

Eighty-three subjects were included (CBS-AD: n = 14; CBS-nAD: n = 17; amnestic AD: n = 29; controls: n = 23). CBS-AD patients had greater whole hippocampal and hippocampal subfield atrophy compared to CBS-nAD. CBS-AD and amnestic AD patients did not differ in subfield volumes. CBS-nAD did not exhibit hippocampal atrophy compared to controls, with the exception of fimbria. (Cohen's d = 1.27; p = 0.038). Presubiculum (Cohen's d = 1.00; p = 0.002) and hippocampal body (Cohen's d = 0.95; p = 0.001) volumes exhibited the greatest differences between CBS-AD and CBS-nAD. Hippocampal subfield volume provided combined sensitivity and specificity < 80% for the discrimination of CBS-AD from CBS-nAD.

CONCLUSION

CBS-AD and amnestic AD patients exhibit comparable, and significantly greater hippocampal atrophy compared to CBS-nAD patients. Hippocampal subfield volumetry in CBS is indicative of an AD underlying pathology.

The Discourse Profile in Corticobasal Syndrome: A Comprehensive Clinical and Biomarker Approach

The aim of this study was to characterize the oral discourse of CBS patients and to verify whether measures obtained during a semi-spontaneous speech production could differentiate CBS patients from controls. A second goal was to compare the performance of patients with CBS probably due to Alzheimer's disease (CBS-AD) pathology and CBS not related to AD (CBS-non-AD) in the same measures, based on the brain metabolic status (FDG-PET) and in the presence of amyloid deposition (amyloid-PET). Results showed that CBS patients were significantly different from controls in speech rate, lexical level, informativeness, and syntactic complexity. Discursive measures did not differentiate CBS-AD from CBS-non-AD. However, CBS-AD displayed more lexical-semantic impairments than controls, a profile that is frequently reported in patients with clinical AD and the logopenic variant of primary progressive aphasia (lvPPA). CBS-non-AD presented mainly with impairments related to motor speech disorders and syntactic complexity, as seen in the non-fluent variant of PPA.

Clinical Spectrum of Tauopathies

Tauopathies are both clinical and pathological heterogeneous disorders characterized by neuronal and/or glial accumulation of misfolded tau protein. It is now well understood that every pathologic tauopathy may present with various clinical phenotypes based on the primary site of involvement and the spread and distribution of the pathology in the nervous system making clinicopathological correlation more and more challenging. The clinical spectrum of tauopathies includes syndromes with a strong association with an underlying primary tauopathy, including Richardson syndrome (RS), corticobasal syndrome (CBS), non-fluent agrammatic primary progressive aphasia (nfaPPA)/apraxia of speech, pure akinesia with gait freezing (PAGF), and behavioral variant frontotemporal dementia (bvFTD), or weak association with an underlying primary tauopathy, including Parkinsonian syndrome, late-onset cerebellar ataxia, primary lateral sclerosis, semantic variant PPA (svPPA), and amnestic syndrome. Here, we discuss clinical syndromes associated with various primary tauopathies and their distinguishing clinical features and new biomarkers becoming available to improve in vivo diagnosis. Although the typical phenotypic clinical presentations lead us to suspect specific underlying pathologies, it is still challenging to differentiate pathology accurately based on clinical findings due to large phenotypic overlaps. Larger pathology-confirmed studies to validate the use of different biomarkers and prospective longitudinal cohorts evaluating detailed clinical, biofluid, and imaging protocols in subjects presenting with heterogenous phenotypes reflecting a variety of suspected underlying pathologies are fundamental for a better understanding of the clinicopathological correlations.

The Significance of Asymmetry in the Assessment of Brain Perfusion in Atypical Tauopathic Parkinsonian Syndromes

Progressive supranuclear palsy syndrome (PSPS) and corticobasal syndrome (CBS) are clinical manifestations of tauopathic Parkinsonian syndromes. Due to their overlapping symptomatology, the differential diagnosis of these entities may be difficult when bounded to clinical assessment. The manifestations are commonly associated with pathological entities—corticobasal degeneration and progressive supranuclear palsy, which are four-repeat tauopathies. In this study, the authors attempted to find whether the asymmetry typically associated with CBS may be feasible in the interpretation of perfusion single-photon computed tomography. The analysis based on the examination of patients with progressive supranuclear palsy—Richardson syndrome (PSP-RS), progressive supranuclear palsy—Parkinsonism predominant (PSP-P), and corticobasal syndrome (CBS) revealed significant asymmetry of perfusion of the amygdala in corticobasal syndrome. The more pronounced abnormalities of perfusion were observed in the left amygdala among patients with more severe Parkinsonian syndromes in CBS on the right. This study shows that the comparison of the perfusion of tauopathic Parkinsonian syndromes should be extended by asymmetry analysis. Interestingly, the differentiating potential of brain perfusion is present in the comparison of CBS and PSP-RS, but not in CBS and PSP-P. This phenomenon could be explained by more distinct asymmetry in the perfusion observed in PSP-P, which diminishes the differentiating potential of this parameter when it comes to the comparison of PSP-P and CBS. To the best of our knowledge, this is the first study evaluating which structures can be interpreted as significantly asymmetrical in the context of perfusion in CBS.

Evolution of Clinical-Pathological Correlations in Early-Onset Alzheimer's Disease Over a 25-Year Period in an Academic Brain Bank

BACKGROUND

Early onset Alzheimer's disease (EOAD) represents a diagnostic challenge and is associated with a high diagnostic delay and misdiagnosis.

OBJECTIVE

To describe clinical and pathological data from a pathologically confirmed EOAD cohort and evaluate evolving trends in clinical-pathological correlation accuracy.

METHODS

Retrospective review of clinical and neuropathological data of pathologically confirmed EOAD patients (age at onset [AAO] < 60). Comparison between two periods: 1994- 2009 and 2010- 2018.

RESULTS

Eighty brain donors were included. Mean AAO, age at death, and diagnostic delay was 55, 66, and 3 years, respectively. Twenty-nine percent had a nonamnestic presentation. Sixteen percent were given a non-AD initial clinical diagnosis (initial misdiagnosis) and 14% received a final misdiagnosis. Nonamnestic presentation patients received more misdiagnoses than amnestic presentation ones (39% versus 7% and 39% versus 3.5%, on initial and final misdiagnosis, respectively). When comparing both time periods, a trend towards a higher diagnostic accuracy in the 2010- 2018 period was observed, mainly on initial misdiagnosis in nonamnestic presentation patients (53% versus 13%, p = 0.069). Diagnostic delay was similar between both periods. Cerebral amyloid angiopathy (96%) and Lewy body co-pathology (55%) were very frequent, while limbic-predominant age-related TDP-43 encephalopathy pathologic changes were only present in 12.5%.

CONCLUSION

In the last decade, there has been a trend towards improved diagnostic accuracy in EOAD, which might be explained by improved diagnostic criteria, increasing experience on EOAD and the beginning of the use of biomarkers, although diagnostic delay remains similar. Concomitant neuropathology was very frequent despite the relatively young age of brain donors.

Neuropathology and emerging biomarkers in corticobasal syndrome

Corticobasal syndrome (CBS) is a clinical syndrome characterised by progressive asymmetric limb rigidity and apraxia with dystonia, myoclonus, cortical sensory loss and alien limb phenomenon. Corticobasal degeneration (CBD) is one of the most common underlying pathologies of CBS, but other disorders, such as progressive supranuclear palsy (PSP), Alzheimer's disease (AD) and frontotemporal lobar degeneration with TDP-43 inclusions, are also associated with this syndrome.In this review, we describe common and rare neuropathological findings in CBS, including tauopathies, synucleinopathies, TDP-43 proteinopathies, fused in sarcoma proteinopathy, prion disease (Creutzfeldt-Jakob disease) and cerebrovascular disease, based on a narrative review of the literature and clinicopathological studies from two brain banks. Genetic mutations associated with CBS, including GRN and MAPT, are also reviewed. Clinicopathological studies on neurodegenerative disorders associated with CBS have shown that regardless of the underlying pathology, frontoparietal, as well as motor and premotor pathology is associated with CBS. Clinical features that can predict the underlying pathology of CBS remain unclear. Using AD-related biomarkers (ie, amyloid and tau positron emission tomography (PET) and fluid biomarkers), CBS caused by AD often can be differentiated from other causes of CBS. Tau PET may help distinguish AD from other tauopathies and non-tauopathies, but it remains challenging to differentiate non-AD tauopathies, especially PSP and CBD. Although the current clinical diagnostic criteria for CBS have suboptimal sensitivity and specificity, emerging biomarkers hold promise for future improvements in the diagnosis of underlying pathology in patients with CBS.

Dissecting the clinical heterogeneity of early-onset Alzheimer's disease

Early-onset Alzheimer's disease (EOAD) is a rare but particularly devastating form of AD. Though notable for its high degree of clinical heterogeneity, EOAD is defined by the same neuropathological hallmarks underlying the more common, late-onset form of AD. In this review, we describe the various clinical syndromes associated with EOAD, including the typical amnestic phenotype as well as atypical variants affecting visuospatial, language, executive, behavioral, and motor functions. We go on to highlight advances in fluid biomarker research and describe how molecular, structural, and functional neuroimaging can be used not only to improve EOAD diagnostic acumen but also enhance our understanding of fundamental pathobiological changes occurring years (and even decades) before the onset of symptoms. In addition, we discuss genetic variation underlying EOAD, including pathogenic variants responsible for the well-known mendelian forms of EOAD as well as variants that may increase risk for the much more common forms of EOAD that are either considered to be sporadic or lack a clear autosomal-dominant inheritance pattern. Intriguingly, specific pathogenic variants in PRNP and MAPT-genes which are more commonly associated with other neurodegenerative diseases-may provide unexpectedly important insights into the formation of AD tau pathology. Genetic analysis of the atypical clinical syndromes associated with EOAD will continue to be challenging given their rarity, but integration of fluid biomarker data, multimodal imaging, and various 'omics techniques and their application to the study of large, multicenter cohorts will enable future discoveries of fundamental mechanisms underlying the development of EOAD and its varied clinical presentations.

Atypical Alzheimer Disease Variants

PURPOSE OF REVIEW

This article discusses the clinical, neuroimaging, and biomarker profiles of sporadic atypical Alzheimer disease (AD) variants, including early-onset AD, posterior cortical atrophy, logopenic variant primary progressive aphasia, dysexecutive variant and behavioral variant AD, and corticobasal syndrome.

RECENT FINDINGS

Significant advances are being made in the recognition and characterization of the syndromically diverse AD variants. These variants are identified by the predominant cognitive and clinical features: early-onset amnestic syndrome, aphasia, visuospatial impairments, dysexecutive and behavioral disturbance, or motor symptoms. Although understanding of regional susceptibility to disease remains in its infancy, visualizing amyloid and tau pathology in vivo and CSF examination of amyloid-β and tau proteins are particularly useful in atypical AD, which can be otherwise prone to misdiagnosis. Large-scale research efforts, such as LEADS (the Longitudinal Early-Onset Alzheimer Disease Study), are currently ongoing and will continue to shed light on our understanding of these diverse presentations.

SUMMARY

Understanding the clinical, neuroimaging, and biomarker profiles of the heterogeneous group of atypical AD syndromes improves diagnostic accuracy in patients who are at increased risk of misdiagnosis. Earlier accurate identification facilitates access to important interventions, social services and disability assistance, and crucial patient and family education.

Dopamine transporter SPECT imaging in corticobasal syndrome: A peak into the underlying pathology?

BACKGROUND

Multiple pathologies may underlie corticobasal syndrome (CBS), including Alzheimer's disease (AD). Dopamine transporter density imaging with Ioflupane ¹²³ I SPECT (DaTscan) may be normal in CBS. No studies to date have examined the relationship between DaTscan status and underlying pathology in CBS.

OBJECTIVES

The main objective of the study was to test whether a normal DaTscan in CBS patients is indicative of an underlying AD pathology, as determined by cerebrospinal fluid (CSF) biomarkers.

METHODS

Eighteen CBS patients were included. They were divided into patients with an AD and a non-AD disease pathology, based on their cerebrospinal fluid biochemical profile. A typical AD CSF profile was defined as an increase in total and phosphorylated at threonine 181 tau protein in addition to a decrease in amyloid-beta with 42 amino acids. DaTscan data were compared in these two groups.

RESULTS

Eight of the 18 CBS patients (44%) had a normal DaTscan. Seven of the 18 CBS patients (39%) had an AD cerebrospinal fluid biochemical profile. Two of seven CBS patients with AD biomarker profile had abnormal DaTscans. Three of 11 CBS patients with a non-AD biomarker profile had normal DaTscans. A normal DaTscan was indicative of AD pathology with suboptimal (~70%) sensitivity and specificity. Semi-quantitative DaTscan analysis did not differentiate between AD from non-AD CSF biomarker profile in CBS.

CONCLUSION

A normal DaTscan is indicative of AD in CBS, but the sensitivity and specificity of DaTscan as an in vivo marker of AD pathology is suboptimal.

Tau deposition patterns are associated with functional connectivity in primary tauopathies

Tau pathology is the main driver of neuronal dysfunction in 4-repeat tauopathies, including cortico-basal degeneration and progressive supranuclear palsy. Tau is assumed to spread prion-like across connected neurons, but the mechanisms of tau propagation are largely elusive in 4-repeat tauopathies, characterized not only by neuronal but also by astroglial and oligodendroglial tau accumulation. Here, we assess whether connectivity is associated with 4R-tau deposition patterns by combining resting-state fMRI connectomics with both 2^nd generation ¹⁸F-PI-2620 tau-PET in 46 patients with clinically diagnosed 4-repeat tauopathies and post-mortem cell-type-specific regional tau assessments from two independent progressive supranuclear palsy patient samples (n = 97 and n = 96). We find that inter-regional connectivity is associated with higher inter-regional correlation of both tau-PET and post-mortem tau levels in 4-repeat tauopathies. In regional cell-type specific post-mortem tau assessments, this association is stronger for neuronal than for astroglial or oligodendroglial tau, suggesting that connectivity is primarily associated with neuronal tau accumulation. Using tau-PET we find further that patient-level tau patterns are associated with the connectivity of subcortical tau epicenters. Together, the current study provides combined in vivo tau-PET and histopathological evidence that brain connectivity is associated with tau deposition patterns in 4-repeat tauopathies.

Differential Diagnosis of Rare Subtypes of Progressive Supranuclear Palsy and PSP-Like Syndromes—Infrequent Manifestations of the Most Common Form of Atypical Parkinsonism

Presently, there is increasing interest in rare PSP (progressive supranuclear palsy) variants, including PSP-PGF (PSP-progressive gait freezing), PSP-PI (PSP-postural instability), PSP-OM (PSP-ocular motor dysfunction), PSP-C (PSP-predominant cerebellar ataxia), PSP-CBS (PSP-corticobasal syndrome), PSP-SL (PSP-speech/language disorders), and PSP-PLS (PSP-primary lateral sclerosis). Diagnosis of these subtypes is usually based on clinical symptoms, thus thorough examination with anamnesis remains a major challenge for clinicians. The individual phenotypes often show great similarity to various neurodegenerative diseases and other genetic, autoimmune, or infectious disorders, manifesting as PSP-mimicking syndromes. At the current stage of knowledge, it is not possible to isolate a specific marker to make a definite ante-mortem diagnosis. The purpose of this review is to discuss recent developments in rare PSP phenotypes and PSP-like syndromes.

Binding characteristics of [18F]PI-2620 distinguish the clinically predicted tau isoform in different tauopathies by PET

The novel tau-PET tracer [¹⁸F]PI-2620 detects the 3/4-repeat-(R)-tauopathy Alzheimer's disease (AD) and the 4R-tauopathies corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP). We determined whether [¹⁸F]PI-2620 binding characteristics deriving from non-invasive reference tissue modelling differentiate 3/4R- and 4R-tauopathies. Ten patients with a 3/4R tauopathy (AD continuum) and 29 patients with a 4R tauopathy (CBS, PSP) were evaluated. [¹⁸F]PI-2620 PET scans were acquired 0-60 min p.i. and the distribution volume ratio (DVR) was calculated. [¹⁸F]PI-2620-positive clusters (DVR ≥ 2.5 SD vs. 11 healthy controls) were evaluated by non-invasive kinetic modelling. R1 (delivery), k2 & k2a (efflux), DVR, 30-60 min standardized-uptake-value-ratios (SUVR_30-60) and the linear slope of post-perfusion phase SUVR (9-60 min p.i.) were compared between 3/4R- and 4R-tauopathies. Cortical clusters of 4R-tau cases indicated higher delivery (R1_SRTM: 0.92 ± 0.21 vs. 0.83 ± 0.10, p = 0.0007), higher efflux (k2_SRTM: 0.17/min ±0.21/min vs. 0.06/min ± 0.07/min, p < 0.0001), lower DVR (1.1 ± 0.1 vs. 1.4 ± 0.2, p < 0.0001), lower SUVR_30-60 (1.3 ± 0.2 vs. 1.8 ± 0.3, p < 0.0001) and flatter slopes of the post-perfusion phase (slope_9-60: 0.006/min ± 0.007/min vs. 0.016/min ± 0.008/min, p < 0.0001) when compared to 3/4R-tau cases. [¹⁸F]PI-2620 binding characteristics in cortical regions differentiate 3/4R- and 4R-tauopathies. Higher tracer clearance indicates less stable binding in 4R tauopathies when compared to 3/4R-tauopathies.

Metabolic and Structural Signatures of Speech and Language Impairment in Corticobasal Syndrome: A Multimodal PET/MRI Study

Introduction: Corticobasal syndrome (CBS) is a progressive neurological disorder related to multiple underlying pathologies, including four-repeat tauopathies, such as corticobasal degeneration and progressive supranuclear palsy, and Alzheimer's disease (AD). Speech and language are commonly impaired, encompassing a broad spectrum of deficits. We aimed to investigate CBS speech and language impairment patterns in light of a multimodal imaging approach.

Materials and Methods: Thirty-one patients with probable CBS were prospectively evaluated concerning their speech–language, cognitive, and motor profiles. They underwent positron emission tomography with [¹⁸F]fluorodeoxyglucose (FDG-PET) and [¹¹C]Pittsburgh Compound-B (PIB-PET) on a hybrid PET-MRI machine to assess their amyloid status. PIB-PET images were classified based on visual and semi-quantitative analyses. Quantitative group analyses were performed on FDG-PET data, and atrophy patterns on MRI were investigated using voxel-based morphometry (VBM). Thirty healthy participants were recruited as imaging controls.

Results: Aphasia was the second most prominent cognitive impairment, presented in 67.7% of the cases, following apraxia (96.8%). We identified a wide linguistic profile, ranging from nonfluent variant-primary progressive aphasia to lexical–semantic deficits, mostly with impaired verbal fluency. PIB-PET was classified as negative (CBS-A– group) in 18/31 (58%) and positive (CBS-A+ group) in 13/31 (42%) patients. The frequency of dysarthria was significantly higher in the CBS-A– group than in the CBS-A+ group (55.6 vs. 7.7%, p = 0.008). CBS patients with dysarthria had a left-sided hypometabolism at frontal regions, with a major cluster at the left inferior frontal gyrus and premotor cortex. They showed brain atrophy mainly at the opercular frontal gyrus and putamen. There was a positive correlation between [¹⁸F]FDG uptake and semantic verbal fluency at the left inferior (p = 0.006, R² = 0.2326), middle (0.0054, R² = 0.2376), and superior temporal gyri (p = 0.0066, R² = 0.2276). Relative to the phonemic verbal fluency, we found a positive correlation at the left frontal opercular gyrus (p = 0.0003, R² = 0.3685), the inferior (p = 0.0004, R² = 0.3537), and the middle temporal gyri (p = 0.0001, R² = 0.3993).

Discussion: In the spectrum of language impairment profile, dysarthria might be helpful to distinguish CBS patients not related to AD. Metabolic and structural signatures depicted from this feature provide further insights into the motor speech production network and are also helpful to differentiate CBS variants.

Pathobiological Subtypes of Alzheimer Disease

Alzheimer disease (AD), the most common form of dementia, is a heterogenous disorder with various pathobiological subtypes. In addition to the 4 major subtypes based on the distribution of tau pathology and brain atrophy (typical, limbic predominant, hippocampal sparing, and minimal atrophy [MA]), several other clinical variants showing distinct regional patterns of tau burden have been identified: nonamnestic, corticobasal syndromal, primary progressive aphasia, posterior cortical atrophy, behavioral/dysexecutive, and mild dementia variants. Among the subtypes, differences were found in age at onset, sex distribution, cognitive status, disease duration, APOE genotype, and biomarker levels. The patterns of key network destructions parallel the tau and atrophy patterns of the AD subgroups essentially. Interruption of key networks, in particular the default-mode network that is responsible for cognitive decline, is consistent in hetero-genous AD groups. AD pathology is often associated with co-pathologies: cerebrovascular lesions, Lewy pathology, and TDP-43 proteinopathies. These mixed pathologies essentially influence the clinical picture of AD and may accel-erate disease progression. Unraveling the heterogeneity among the AD spectrum entities is important for opening a window to pathogenic mechanisms affecting the brain and enabling precision medicine approaches as a basis for developing preventive and ultimately successful disease-modifying therapies for AD.

Clinical Phenotypes in Corticobasal Syndrome with or without Amyloidosis Biomarkers

Corticobasal syndrome (CBS) is a neuropathologically heterogeneous entity. The use of cerebrospinal fluid and amyloid biomarkers enables detection of underlying Alzheimer's disease (AD) pathology. We thus compared clinical, eye movement, and 18FDG-PET imaging characteristics in CBS in two groups of patients divided according to their amyloid biomarkers profile. Fourteen patients presenting with CBS and amyloidosis (CBS-A+) were compared with 16 CBS patients without amyloidosis (CBS-A-). The two groups showed similar motor abnormalities (parkinsonism, dystonia) and global cognitive functions. Unlike CBS-A+ patients who displayed more posterior cortical abnormalities, CBS-A- patients demonstrated more anterior cortical and brain stem dysfunctions on the basis of neuropsychological testing, study of saccade velocities and brain hypometabolism areas on 18FDG-PET. Interestingly, Dopamine Transporter SPECT imaging showed similar levels of dopaminergic degeneration in both groups. These findings confirm common and distinct brain abnormalities between the different neurodegenerative diseases that result in CBS. We demonstrate the importance of a multidisciplinary approach to improve diagnosis in vivo in particular on oculomotor examination.

A systematic review of atypical Alzheimer's disease including behavioural and psychological symptoms

Alzheimer's disease (AD) is the commonest cause of dementia, characterized by the clinical presentation of progressive anterograde episodic memory impairment. However, atypical presentation of patients is increasingly recognized. These atypical AD include logopenic aphasia, behavioural variant AD, posterior cortical atrophy, and corticobasal syndrome. These atypical AD are more common in patients with young onset AD before the age of 65 years old. Since medical needs (including the behavioural and psychological symptoms of dementia) of atypical AD patients could be different from typical AD patients, it is important for clinicians to be aware of these atypical forms of AD. In addition, disease modifying treatment may be available in the future. This review aims at providing an update on various important subtypes of atypical AD including behavioural and psychological symptoms.

New insights into atypical Alzheimer's disease in the era of biomarkers

Most patients with Alzheimer's disease present with amnestic problems; however, a substantial proportion, over-represented in young-onset cases, have atypical phenotypes including predominant visual, language, executive, behavioural, or motor dysfunction. In the past, these individuals often received a late diagnosis; however, availability of CSF and PET biomarkers of Alzheimer's disease pathologies and incorporation of atypical forms of Alzheimer's disease into new diagnostic criteria increasingly allows them to be more confidently diagnosed early in their illness. This early diagnosis in turn allows patients to be offered tailored information, appropriate care and support, and individualised treatment plans. These advances will provide improved access to clinical trials, which often exclude atypical phenotypes. Research into atypical Alzheimer's disease has revealed previously unrecognised neuropathological heterogeneity across the Alzheimer's disease spectrum. Neuroimaging, genetic, biomarker, and basic science studies are providing key insights into the factors that might drive selective vulnerability of differing brain networks, with potential mechanistic implications for understanding typical late-onset Alzheimer's disease.

An autopsy case of corticobasal syndrome due to asymmetric degeneration of the motor cortex and substantia nigra with TDP-43 proteinopathy, associated with Alzheimer's disease pathology

We herein report a case of corticobasal syndrome (CBS) due to asymmetric degeneration of the motor cortex and substantia nigra with transactivation response DNA-binding protein of 43 kDa (TDP-43) proteinopathy, associated with Alzheimer's disease (AD) pathology. An 85-year-old man initially noticed that he had difficulty in walking and had trouble in moving his right hand and lower limb one year later. His gait disturbance was aggravated, and at the age of 87 years, his neurological examination revealed parkinsonism and positive frontal lobe signs. Brain magnetic resonance imaging (MRI) revealed atrophy of the left frontotemporal lobe and cerebral peduncle, and cerebral blood flow scintigraphy revealed hypoperfusion of the left frontotemporal lobe, leading to a possible diagnosis of CBS. At the age of 89 years, he was bedridden, and rarely spoke. He died of aspiration pneumonia five years after the onset of initial symptoms. At the autopsy, the brain weighed 1280 g and showed left-sided hemiatrophy of the cerebrum and cerebral peduncle. Neuropathological examination revealed AD pathology (Braak AT8 stage V, Braak stage C, CERAD B, Thal classification 5). Phosphorylated TDP-43 (p-TDP-43) immunohistochemistry revealed widespread deposits of dystrophic neurites (DNs), glial cytoplasmic inclusions (GCIs), and neuronal cytoplasmic inclusions (NCIs), which were most remarkable in layers II/III of the motor cortex and predominant on the left hemisphere of the frontal cortex, these neuropathology being consistent with frontotemporal lobar degeneration with TDP-43 (FTLD-TDP) type A. Interestingly, neuronal loss in the substantia nigra was more severe on the left than the right side, with a few phosphorylated tau (p-tau) and p-TDP-43 deposits. It is highly likely that asymmetric TDP-43 pathology rather than symmetric tau pathology contributed to the laterality of degeneration of the cerebral cortex, substantia nigra, and pyramidal tract, which led us to suggest that TDP-43 proteinopathy might be a primary cause.

FDG-PET Patterns Predict Amyloid Deposition and Clinical Profile in Corticobasal Syndrome

BACKGROUND

Corticobasal syndrome (CBS) is an atypical parkinsonian syndrome related to multiple underlying pathologies.

OBJECTIVE

To investigate if individual brain [¹⁸ F]fluorodeoxyglucose-positron emission tomography (FDG-PET) patterns could distinguish CBS due to Alzheimer's disease (AD) from other pathologies based on [¹¹ C]Pittsburgh Compound-B (PIB)-PET.

METHODS

Forty-five patients with probable CBS were prospectively evaluated regarding cognitive and movement disorders profile. They underwent FDG-PET and were distributed into groups: likely related to AD (CBS FDG-AD) or likely non-AD (CBS FDG-nonAD) pathology. Thirty patients underwent PIB-PET on a hybrid PET-magnetic resonance imaging equipment to assess their amyloid status. FDG and PIB-PET images were classified individually based on visual and semi-quantitative analysis, blinded to each other. Quantitative group analyses were also performed.

RESULTS

CBS FDG-AD group demonstrated worse cognitive performances, mostly concerning attention, memory, visuospatial domains, and displayed more myoclonus and hallucinations. The non-AD metabolic group presented more often limb dystonia, ocular motor dysfunction, motor perseveration, and dysarthria. All patients classified as CBS FDG-AD tested positive at PIB-PET compared to 3 of 20 in the non-AD group. The individual FDG-PET classification demonstrated 76.92% of sensitivity, 100% of specificity and positive predictive value and 88.5% of balanced accuracy to detect positive PIB-PET scans. Individuals with positive and negative PIB-PET showed hypometabolism in posterior temporoparietal areas and in thalamus and brainstem, respectively, mainly contralateral to most affected side, disclosing possible metabolic signatures of CBS variants.

CONCLUSION

FDG-PET was useful to predict AD and non-AD CBS variants depicting their specific degeneration patterns, different clinical features, and brain amyloid deposition. © 2020 International Parkinson and Movement Disorder Society.

Neuropathological assessment of the Alzheimer spectrum

Alzheimer disease (AD), the most common form of dementia globally, classically defined a clinicopathological entity, is a heterogenous disorder with various pathobiological subtypes, currently referred to as Alzheimer continuum. Its morphological hallmarks are extracellular parenchymal β-amyloid (amyloid plaques) and intraneuronal (tau aggregates forming neurofibrillary tangles) lesions accompanied by synaptic loss and vascular amyloid deposits, that are essential for the pathological diagnosis of AD. In addition to "classical" AD, several subtypes with characteristic regional patterns of tau pathology have been described that show distinct clinical features, differences in age, sex distribution, biomarker levels, and patterns of key network destructions responsible for cognitive decline. AD is a mixed proteinopathy (amyloid and tau), frequently associated with other age-related co-pathologies, such as cerebrovascular lesions, Lewy and TDP-43 pathologies, hippocampal sclerosis, or argyrophilic grain disease. These and other co-pathologies essentially influence the clinical picture of AD and may accelerate disease progression. The purpose of this review is to provide a critical overview of AD pathology, its defining pathological substrates, and the heterogeneity among the Alzheimer spectrum entities that may provide a broader diagnostic coverage of this devastating disorder as a basis for implementing precision medicine approaches and for ultimate development of successful disease-modifying drugs for AD.

PET Tau Imaging and Motor Impairments Differ Between Corticobasal Syndrome and Progressive Supranuclear Palsy With and Without Alzheimer's Disease Biomarkers

Introduction: Frontotemporal lobar degeneration (FTLD)-related syndrome includes progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS). PSP is usually caused by a tauopathy but can have associated Alzheimer's disease (AD) while CBS can be caused by tauopathy, transactive response DNA binding protein 43 kDa, or AD pathology. Our aim was to compare the parkinsonian syndromes presenting without AD biomarkers (CBS/PSP-non-AD) to parkinsonian syndromes with AD biomarkers (CBS/PSP-AD).

Materials and Methods: Twenty-four patients [11 males, 13 females; age (68.46 ± 7.23)] were recruited for this study. The whole cohort was divided into parkinsonian syndromes without AD biomarkers [N = 17; diagnoses (6 CBS, 11 PSP)] and parkinsonian syndromes with AD biomarkers [N = 7; diagnoses (6 CBS-AD, 1 PSP-AD)]. Anatomical MRI and PET imaging with tau ligand [18F]-AV1451 tracer was completed. Cerebrospinal fluid analysis or [18F]-AV1451 PET imaging was used to assess for the presence of AD biomarkers. Progressive supranuclear palsy rating scale (PSPRS) and unified Parkinson's disease rating scale (UPDRS) motor exam were implemented to assess for motor disturbances. Language and cognitive testing were completed.

Results: The CBS/PSP-non-AD group [age (70.18 ± 6.65)] was significantly older (p = 0.028) than the CBS/PSP-AD group [age (64.29 ± 7.32)]. There were no differences between the groups in terms of gender, education, years of disease duration, and disease severity as measured with the Clinical Dementia Rating scale. The CBS/PSP-non-AD group had significantly lower PET Tau Standard Volume Uptake Ratio (SUVR) values compared to the CBS/PSP-AD group in multiple frontal and temporal areas, and inferior parietal (all p < 0.03). The CBS/PSP-non-AD group had significantly higher scores compared to the CBS/PSP-AD group on PSPRS (p = 0.004) and UPDRS motor exam (p = 0.045). The CBS/PSP-non-AD group had higher volumes of inferior parietal, precuneus, and hippocampus (all p < 0.02), but lower volume of midbrain (p = 0.02), compared to the CBS/PSP-AD group.

Discussion: The CBS/PSP-non-AD group had higher motor disturbances compared to the CBS/PSP-AD group; however, both groups performed similarly on neuropsychological measures. The AD biomarker group had increased global uptake of PET Tau SUVR and lower volumes in AD-specific areas. These results show that the presenting phenotype of CBS and PSP syndromes and the distribution of injury are strongly affected by the presence of AD biomarkers.

MRI and flortaucipir relationships in Alzheimer's phenotypes are heterogeneous

OBJECTIVE

To assess the relationships between MRI volumetry and [18 F]flortaucipir PET of typical and atypical clinical phenotypes of Alzheimer's disease, by genarian (age by decade).

METHODS

Five-hundred and sixty-four participants including those with typical (n = 86) or atypical (n = 80) Alzheimer's dementia and normal controls (n = 398) underwent apolipoprotein E genotyping, MRI, flortaucipir, and 11 C-PiB; all 166 Alzheimer's participants were beta-amyloid positive and all controls were beta-amyloid negative. Grey matter volume and flortaucipir standard uptake value ratios were calculated for hippocampus, entorhinal cortex, and neocortex. Ratios of hippocampal-to-neocortical and entorhinal-to-neocortical volume and flortaucipir uptake were also calculated. Linear regression models assessed relationships among regional volume, flortaucipir uptake, and ratios and phenotypes, within three genarians (50-59, 60-69, and 70+). Voxel-level analyses were also performed.

RESULTS

For 50-59 greater medial temporal atrophy and flortaucipir uptake was observed in the typical compared with atypical phenotype. The typical phenotype also showed greater frontal neocortex uptake with the voxel-level analysis. For 60-69 and 70+ there was greater hippocampal volume loss in the typical compared with atypical phenotype while only the 60-69, but not the 70+ group, showed a difference in hippocampal flortaucipir uptake. We also observed a pattern for higher neocortical flortaucipir uptake to correlate with younger age decade for both phenotypes.

INTERPRETATION

MRI volumetry versus flortaucipir PET relationships differ across Alzheimer's clinical phenotypes, and also within phenotype across age decades. This suggests that there is potential risk of masked effects by not accounting for genarian in participants with beta-amyloid and tau-positive biomarker defined Alzheimer's disease.

The path to biomarker-based diagnostic criteria for the spectrum of neurodegenerative diseases

Introduction: The postmortem examination still represents the reference standard for detecting the pathological nature of chronic neurodegenerative diseases (NDD). This approach displays intrinsic conceptual limitations since NDD represent a dynamic spectrum of partially overlapping phenotypes, shared pathomechanistic alterations that often give rise to mixed pathologies.Areas covered: We scrutinized the international clinical diagnostic criteria of NDD and the literature to provide a roadmap toward a biomarker-based classification of the NDD spectrum. A few pathophysiological biomarkers have been established for NDD. These are time-consuming, invasive, and not suitable for preclinical detection. Candidate screening biomarkers are gaining momentum. Blood neurofilament light-chain represents a robust first-line tool to detect neurodegeneration tout court and serum progranulin helps detect genetic frontotemporal dementia. Ultrasensitive assays and retinal scans may identify Aβ pathology early, in blood and the eye, respectively. Ultrasound also represents a minimally invasive option to investigate the substantia nigra. Protein misfolding amplification assays may accurately detect α-synuclein in biofluids.Expert opinion: Data-driven strategies using quantitative rather than categorical variables may be more reliable for quantification of contributions from pathophysiological mechanisms and their spatial-temporal evolution. A systems biology approach is suitable to untangle the dynamics triggering loss of proteostasis, driving neurodegeneration and clinical evolution.

Parkinsonism in genetic and sporadic Alzheimer's disease

Alzheimer disease (AD) is a neurodegenerative disease characterized by deposition of pathologically aggregated amyloid-β in the extracellular space and pathologically aggregated tau protein in the intracellular space. Mainly affected brain areas are the temporal and the parietal lobe, which cause the classical AD phenotype consisting of increasing forgetfulness and difficulties to orientate. However, AD pathology is not restricted to these brain areas and spreads through the brain as the disease progresses, which can lead to a number of additional symptoms and to atypical presentations. Motor symptoms in AD are the topic of this chapter. Even though motor symptoms are usually not severe and seldomly treated, motor symptoms are quite frequent and can be observed in the majority of AD cases. Motor symptoms are especially frequent in cases with early onset and long disease duration, for example in Apolipoprotein E e4 carriers and in familial early onset AD. In severe cases treatment with pharmacological approaches might be considered. However, treatment strategies largely rely on expert opinions. Due to potential positive impact on prognosis non-pharmacological treatment and exercise might be considered in less advanced cases.